Change default_frames_limit trough Text Editor script
Its the clip associated with the space.
Similarly to a text in the text editor, an image in the image editor, what is known as the context.clip in the movie clip editor, is the clip assigned to the space.
To the python console:
Loop thru the screens to find a movie clip area and return its active space.
&gt;&gt;&gt; def get_clip():
...     for s in D.screens:
...         for a in s.areas:
...             if a.type == 'CLIP_EDITOR':
...                 return a.spaces.active
...     return None
...     
&gt;&gt;&gt; mc = get_clip()
&gt;&gt;&gt; mc
bpy.data.screens['Default.002']...SpaceClipEditor

The active clip of that space
&gt;&gt;&gt; clip = mc.clip
&gt;&gt;&gt; clip
bpy.data.movieclips['Batman_(1966)_S01E01.mkv']

&gt;&gt;&gt; clip.tracking.tracks.data.settings.default_frames_limit
0